1. Field of the Invention
The present invention relates to a encoder and a decoder considered for the next generation mobile communication system requiring high channel coding performance, in particular to a concatenated convolutional encoder and a decoder of a mobile communication system which is capable of providing a dual mode encoder and a decoder for supporting both a parallel concatenated convolutional code and a serially concatenated convolutional code and improving the performance of the system by using punctured and thrown away sequence in a convolutional encoder.
2. Description of the Prior Art
In a mobile communication system according to the conventional technology, a turbo encoder showing high performance is used for low SNR (Signal to Noise Ratio).
The turbo encoder comprises a parallel concatenated convolutional encoder and a serially concatenated convolutional encoder.
Between them, the serially concatenated convolutional encoder showing continual performance improvement stood in the spotlight because the parallel concatenated convolutional encoder shows a performance saturation phenomenon in high SNR.
The serially concatenated convolutional encoder will now be described with reference to accompanying FIG. 1.
FIG. 1 is a construction profile illustrating the conventional serially concatenated convolutional encoder of the mobile communication system.
As depicted in FIG. 1, the conventional serially 3 of the mobile communication system comprises a first RSC (Recursive Systematic Convolutional) encoder 11 for coding an inputted data sequence DO with 1/2 code rate, a puncturer 12 for puncturing a code outputted from the first RSC encoder 11 with a puncturing pattern 1110 and outputting it, an interleaver 13 for lowering correlation between adjacent data by relocating position of the code outputted from the puncturer 12 after being punctured, and a second RSC encoder 14 for decoding the code relocated by the interleaver 13 with the 1/2 decode rate and outputting the final code CO.
The operation will now be described in detail.
First, when the data sequence DO is inputted to the first RSC encoder 11, the first RSC encoder 11 codes the inputted data sequence DO with 1/2 code rate, generates two new sequences and outputs them. Herein, the two sequences outputted from the first RSC encoder 11 are combined as one sequence by a switch (not shown), and is provided to the puncturer 12.
After that, the puncturer 12 punctures the sequence outputted from the first RSC encoder 11 with the puncturing pattern 1110, and outputs it to the interleaver 13.
Herein, in the puncturing pattern 1110, “1” means the data outputted from the first RSC encoder 11 is outputted to the interleaver 13 as it is, and “0” means the data outputted from the first RSC encoder 11 is punctured, in other words, it is thrown away.
After all, when 4 bits data is outputted from the first RSC encoder 11, the fourth data is thrown away (punctured), and the rest 3 bits are passed.
In addition, the interleaver 13 randomly relocates the data punctured on the multiple proportion bit of 4, reads it to a column direction, and outputs it. Accordingly the interleaver can lower the correlation between the adjacent codes and outputs it to the second RSC encoder 14.
The second RSC encoder 14 codes the code outputted from the interleaver 13 with 1/2 code rate, generates new two sequences, and outputs them. Herein, the outputted two sequences are added by a switch (not shown) as one sequence, and is outputted a's a final coded code CO.
Herein, in the conventional serially concatenated convolutional encoder, a encoder of which constraint length is 3 and 1/2 code rate is used, the first RSC encoder 11 and second RSC encoder 14 use the encoder having same construction.
Meanwhile, the conventional parallel concatenated convolutional encoder comprises two RSC encoders and an interleaver. In other words, in the conventional coding technology, after the input sequence of the first convolutional encoder is relocated through the interleaver, the sequence is used as an input sequence of the second convolutional encoder.
Accordingly, because only data part of the output of the first convolutional encoder can be provided to the input of the second convolutional encoder, the system performance lowering problem occurs in the SNR increasing region, accordingly the credibility of the system lowers due to that.
As described above in detail, in the conventional technology, the input sequence of the first convolutional encoder and second convolutional encoder have same weight values, in particular when the weight value is 2, a code having low weight value about a certain sequence pattern is generated according to the characteristic of the RSC encoder.
In addition, in the conventional technology, because only data part of the output of the first convolutional encoder can be provided to the input of the second convolutional encoder, accordingly the sudden performance lowering problem occurs in the high SNR region.
In addition, in the conventional technology, because the sudden performance lowering problem occurs in the SNR increasing region, accordingly there is a credibility lowering problem due to that.
In addition, in the conventional technology, in the parallel concatenated convolutional encoder, extrinsic information transmitted/received between the each module in iterative decoding only deals with information about the input sequence to the exclusion of information about parity sequence.
In addition, in the conventional technology, the performance of the system lowers due to the sequence punctured by the serially concatenated convolutional encoder.